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{{Short description|French analog color television system}}
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{{Analog television encoding systems by nation}}
'''SECAM''', also written '''SÉCAM''' ({{IPA|fr|sekam}}, ''Système Électronique Couleur Avec Mémoire'', French for ''electronic colour system with memory''), is an [[analog television|analogue colour television]] system that was used in France, Russia, and some other countries or territories of Europe and Africa. It was one of three major analog colour television standards, the others being [[PAL]] and [[NTSC]]. Similar to PAL, a SECAM picture is made up of 625 interlaced lines and displayed at a rate of 25 frames per second (except SECAM-M). However, because of how SECAM processes colour information, it is not compatible with the PAL video format standard. SECAM video is [[composite video]]; the [[Luma (video)|luminance]] (luma, monochrome image) and [[chrominance]] (chroma, colour applied to the monochrome image) are transmitted together as one signal.

All the countries using SECAM have either converted to [[Digital Video Broadcasting]] (DVB), the new pan-European standard for digital television, or are currently in the [[Digital television transition|process of conversion]]. SECAM remained a major standard into the 2000s.

== History ==
[[File:Chromat-2062 Farbfernseher 6400dpi 1979.jpg|thumb|''Chromat 2062'', East German–produced dual-standard PAL/SECAM TV set]]

=== Invention ===
Development of SECAM predates PAL, and began in 1956 by a team led by [[Henri de France]] working at ''Compagnie Française de Télévision'' (later bought by Thomson, now [[Vantiva|Technicolor]]). NTSC was considered undesirable in Europe because of its tint problem, requiring an additional [[tint control|control]], which SECAM (and PAL) solved.

Some have argued that the primary motivation for the development of SECAM in France was to [[protectionism|protect]] French television equipment manufacturers.<ref>Crane, R. J. (1979). The Politics of International Standards: France and the Color TV War, Ablex Publishing Corporation.</ref> However, incompatibility had started with the earlier unusual decision to adopt positive [[video modulation]] for 819-line French broadcast signals (only the UK's [[405-line]] was similar; widely adopted [[525 lines|525-]] and [[625-line]] systems used negative video).

The first proposed system was called SECAM I in 1961, followed by other studies to improve compatibility and image quality,<ref name="auto4" /> but it was too soon for a wide introduction. A version of SECAM for the French [[819 line|819-line television standard]] was devised and tested, but never introduced.<ref>{{cite web |title=France had a national HD TV system as far back as 1949 |url=https://www.redsharknews.com/business/item/471-france-had-a-national-hd-tv-system-in-1949 |url-status=live |archive-url=https://web.archive.org/web/20211213082818/https://www.redsharknews.com/business/item/471-france-had-a-national-hd-tv-system-in-1949 |archive-date=13 December 2021 |access-date=13 December 2021}}</ref>

Following a pan-European agreement to introduce colour TV only on 625-line broadcasts, France had to switch to that system, which happened in 1963 with the introduction of "la deuxième chaîne ORTF" [[France 2]], the second national TV network.

Further improvements during 1963 and 1964 to the standard were called SECAM II<ref name="auto4" /> and SECAM III, with the latter being presented at the 1965 [[ITU-R|CCIR]] General Assembly in [[Vienna]], and adopted by France and the [[Soviet Union]].<ref name="auto4" /><ref name="auto2">{{cite news |date=15 July 1966 |title=Londres et Bonn repoussent une suggestion franco-soviétique en faveur du procédé S.E.C.A.M.-IV |url=https://www.lemonde.fr/archives/article/1966/07/15/londres-et-bonn-repoussent-une-suggestion-franco-sovietique-en-faveur-du-procede-s-e-c-a-m-iv_2691879_1819218.html |url-status=live |archive-url=https://web.archive.org/web/20220515005816/https://www.lemonde.fr/archives/article/1966/07/15/londres-et-bonn-repoussent-une-suggestion-franco-sovietique-en-faveur-du-procede-s-e-c-a-m-iv_2691879_1819218.html |archive-date=15 May 2022 |access-date=15 May 2022 |newspaper=Le Monde}}</ref>

Soviet technicians were involved in a separate development of the standard, creating an incompatible variant called NIIR or SECAM IV,<ref name="auto4">{{cite web |title=Bloomsbury Collections – History of Technology – Volume Twenty, 1998 |url=https://www.bloomsburycollections.com/book/history-of-technology-volume-20-volume-twenty-1998/the-pal-secam-colour-television-controversy?from=search |website=bloomsburycollections.com |archive-url=https://web.archive.org/web/20180604052032/https://www.bloomsburycollections.com/book/history-of-technology-volume-20-volume-twenty-1998/the-pal-secam-colour-television-controversy |archive-date=4 June 2018}}</ref> which was not deployed. The team was working in [[Moscow]]'s [[Telecentrum]]. The NIIR designation comes from the name of the ''[[Nautchno-Issledovatelskiy Institut Radio]]'' (''NIIR'', ''rus.'' Научно-Исследовательский Институт Радио), a Soviet research institute involved in the studies.<ref name="auto2" /> Two standards were developed: ''Non-linear NIIR'',<ref name="auto3">{{cite web |title=Sowjetisch Russisches Farbfernsehen SECAM IV Linear NIR NIIR-Farbfernsehsystem NIR 4 |url=http://www.scheida.at/scheida/Televisionen_CCCP_II_UdSSRII.htm |url-status=live |archive-url=https://web.archive.org/web/20211127055943/http://www.scheida.at/scheida/Televisionen_CCCP_II_UdSSRII.htm |archive-date=27 November 2021 |access-date=15 May 2022 |website=scheida.at}}</ref> in which a process analogous to [[gamma correction]] is used, and ''Linear NIIR''<ref name="auto3" /> or ''SECAM IV'' that omits this process.<ref>[http://www.pembers.freeserve.co.uk/World-TV-Standards/Colour-Standards.html#SECAM-IV SECAM-IV] {{webarchive |url=https://web.archive.org/web/20140221112432/http://www.pembers.freeserve.co.uk/World-TV-Standards/Colour-Standards.html |date=21 February 2014}}</ref> SECAM IV was proposed by France and USSR at the 1966 Oslo CCIR conference<ref name="auto4" /><ref name="auto2" /> and demonstrated in London.<ref>{{cite web |author=Jack Gould |date=17 March 1966 |title=TV: Soviet Union Offers Color System; B.B.C. Tests Secam IV, Amplitude Modulator Moscow and Paris Balk at Favored FM Device |url=https://www.nytimes.com/1966/03/17/archives/tv-soviet-union-offers-color-system-bbc-tests-secam-iv-amplitude.html |url-status=live |archive-url=https://web.archive.org/web/20220515005816/https://www.nytimes.com/1966/03/17/archives/tv-soviet-union-offers-color-system-bbc-tests-secam-iv-amplitude.html |archive-date=15 May 2022 |access-date=15 May 2022 |work=The New York Times}}</ref>

Further improvements were SECAM III A, followed by SECAM III B,<ref name="auto4" /> the system adopted for general use in 1967.

=== Implementation ===
Tested until 1963 on the second French national network "la deuxième chaîne ORTF", the SECAM standard was adopted in [[France]] and launched on 1 October 1967, now called France 2. A group of four suited men—a presenter ([[Georges Gorse]], Minister of Information) and three contributors to the system's development—were shown standing in a studio. Following a count from 10, at 2:15&nbsp;pm the black-and-white image switched to colour; the presenter then declared "''Et voici la couleur !''" (fr: And here is colour!)<ref>{{cite web |title=INA: Présentation officielle de la télévision couleur |url=http://www.ina.fr/video/CPF86633716/presentation-officielle-de-la-television-couleur.fr.html |url-status=live |archive-url=https://web.archive.org/web/20110520171238/http://www.ina.fr/video/CPF86633716/presentation-officielle-de-la-television-couleur.fr.html |archive-date=20 May 2011 |access-date=4 August 2014}}</ref> In the same year of 1967, CLT of [[Lebanon]] became the third television station in the world, after {{ill|ORTF Television 2|fr|Deuxième chaîne de l'ORTF|lt=RTF Télévision 2}} in [[France]] and the [[Soviet Central Television]] in the [[Soviet Union]], to broadcast in colour utilizing the French SECAM technology.<ref>{{cite book |last1=Harb |first1=Zahera |title=Channels of resistance in Lebanon: liberation propaganda, Hezbollah and the media |date=2011 |publisher=Tauris |isbn=978-1-84885-120-7 |location=London [etc.] |page=95}}</ref>

The first colour television sets cost 5000 French new francs (the change to new franc occurred in 1960; see [[French franc|francs]] for more details). At that time a pocket book costed roughly 1 NF.{{Citation needed|date=July 2025}}

Colour TV was not very popular initially; only about 1500 people watched the inaugural program in colour. A year later in 1968, only 200,000 sets had been sold of an expected million. This pattern was similar to the earlier slow build-up of colour television popularity in the US.{{Synthesis inline|date=May 2024}}

In March 1969, [[East Germany]] decided to adopt SECAM III B.<ref name="auto4" /> The adoption of SECAM in Eastern Europe has been attributed to [[Cold War]] political machinations. According to this explanation, East German political authorities were well aware of West German television's popularity and adopted SECAM rather than the PAL encoding used in [[West Germany]].<ref>{{cite book |last=Glaubitz |first=Gerald |title=Die PAL-SECAM-Kontroverse in der DDR: Die politisch-ideologische Instrumentalisierung der Farbfernsehfrage durch den ostdeutschen Staat zwischen 1965 und 1969 |publisher=GNT-Verlag |year=2004 |isbn=978-3928186735 |location=Diepholz}}</ref> This did not hinder mutual reception in black and white, because the underlying TV standards remained essentially the same in both parts of Germany. However, [[East Germans]] responded by buying PAL decoders for their SECAM sets. Eventually, the government in East Berlin stopped paying attention to so-called "[[Republikflucht]] via Fernsehen", or "defection via television". Later East German-produced TV sets, such as the [[:de:Chromat (Fernsehgerät)|RFT Chromat]], even included a dual-standard PAL/SECAM decoder as an option.

Another explanation for the Eastern European adoption of SECAM, led by the Soviet Union, is that the Russians had extremely long distribution lines between broadcasting stations and transmitters.<ref>{{cite web |date=25 July 1963 |title=Colour Television for Europe, New Scientist, 23 July 1963 |url=https://books.google.com/books?id=bmtByFnNCOQC&pg=PA197}}</ref> Long co-axial cables or microwave links can cause amplitude and phase variations, which do not affect SECAM signals.

Other countries, notably the [[United Kingdom]] and [[Italy]], briefly experimented with SECAM before opting for PAL. SECAM was adopted by former French and [[Belgium|Belgian]] colonies in [[Africa]], as well as [[Greece]], [[Cyprus]], and [[Eastern Bloc]] countries (except for [[Romania]]), and some [[Middle East]]ern countries.{{Citation needed|date=May 2024}}

European efforts during the 1980–90s toward the creation of a unified analogue standard, resulting in the [[Multiplexed Analogue Components|MAC standards]], still used the sequential colour transmission idea of SECAM, with only one of time-compressed [[Y′UV|U and V components]] being transmitted on a given line. The [[D2-MAC]] standard enjoyed some short real market deployment, particularly in northern European countries. To some extent, this idea is still present in [[Chroma subsampling|4:2:0]] digital sampling format, which is used by most [[digital video]] media available to the public. In this case, however, colour resolution is halved in both horizontal and vertical directions thus yielding a more symmetrical behavior.

=== Decline ===
With the [[fall of communism]] and following a period when multi-standard TV sets became common in the early 2000s, many Central and Eastern European countries decided to switch to the West German-developed PAL system. Yet SECAM remained in use in [[Russia]], [[Belarus]],<ref>{{cite web |title=Samsung TV – PAL / NTSC / SECAM Countries List {{!}} Samsung Support CA |url=https://www.samsung.com/ca/support/tv-audio-video/can-i-use-my-tv-in-another-country/ |url-status=live |archive-url=https://web.archive.org/web/20201022043856/https://www.samsung.com/ca/support/tv-audio-video/can-i-use-my-tv-in-another-country/ |archive-date=22 October 2020 |access-date=2020-10-18 |website=Samsung ca |language=en-CA}}</ref> and the French-speaking African countries. In the late 2000s, SECAM started a process of being phased out and replaced by [[DVB]].

Unlike some other manufacturers, the company where SECAM was invented, [[Vantiva|Technicolor]] (known as Thomson until 2010), still sold television sets worldwide under different brands until the company sold its Trademark Licensing operations in 2022; this may be due in part to the legacy of SECAM. Thomson bought the company that developed PAL, Telefunken, and even co-owned the [[RCA Corporation|RCA]] brand – RCA being the creator of NTSC. Thomson also co-authored the [[ATSC standards]] which are used for American [[high-definition television]].

== Design ==
[[File:Spectre SECAM NICAM.png|thumb|400px|Spectrum of a SECAM broadcast, with colour (red) and sound (green, yellow) sub-carrier frequencies]]
Just as with the other colour standards adopted for broadcast usage over the world, SECAM is a standard that permits existing monochrome television receivers predating its introduction to continue to be operated as monochrome televisions. Because of this compatibility requirement, colour standards added a second signal to the basic monochrome signal, which carries the colour information. The black-and-white information is called the [[luma (video)|luminance]] or <math>Y</math> for short, and the colour information is called [[chrominance]] or <math>C</math> for short. Monochrome television receivers only display luminance, while colour receivers process both signals. The [[YDbDr]] [[colour space]] is used to encode the mentioned <math>Y</math> (luminance) and <math>D_BD_R</math> ([[R-Y|red]] and [[B-Y|blue colour difference]] signals that make up chrominance) components.

Additionally, for compatibility, it is required to use no more [[Bandwidth (signal processing)|bandwidth]] than the monochrome signal alone; the colour signal has to be somehow inserted into the monochrome signal, without disturbing it. This insertion is possible because the [[Bandwidth (signal processing)|bandwidth]] of the monochrome TV signal is generally not fully utilized; the high-frequency portions of the signal, corresponding to fine details in the image, were often not recorded by contemporary video equipment, or not visible on consumer televisions anyway, especially after transmission. This section of the [[spectrum]] was thus used to carry colour information, at the cost of reducing the possible [[Image resolution|resolution]].

European monochrome standards were not compatible when SECAM was first being considered. France had introduced an [[819 line|819-line system]] that used [[CCIR System E|14&nbsp;MHz of bandwidth]] (System E), much more than the [[CCIR System A|5&nbsp;MHz standard]] used in the UK (System A) or the [[CCIR System M|6&nbsp;MHz]] in the US (System M). The closest thing to a standard in Europe at the time was the [[CCIR System D|8&nbsp;MHz 625-line system]] (System D), which had originated [[Germany]] and the [[Soviet Union]] and quickly became one of the most used systems. An effort to harmonize European broadcasts on the [[625-line]] system started in the 1950s and was first implemented in [[CCIR System I|Ireland]] in 1962 (System I).

SECAM thus had the added issue of having to be compatible both with their existing 819-line system as well as their future broadcasts on the 625-line system. As the latter used much less bandwidth, it was this standard that defined the amount of colour information that could be carried. In the 8&nbsp;MHz standard, the signal is split into two parts, the video signal, and the audio signal, each with its own [[carrier frequency]]. For any given channel, one carrier is located 1.25&nbsp;MHz above the [[Broadcast band|channel's listed frequency]] and indicates the location of the luminance portion of the signal. A second carrier is located 6&nbsp;MHz above the luma carrier, indicating the center of the audio signal.

To add colour to the signal, SECAM adds another carrier located 4.4336...&nbsp;MHz above the luma carrier. The chroma signal is centered on this carrier, overlapping the upper part of the luma frequency range. Because the information of most [[scan line]]s differ little from their immediate neighbors, both luma and chroma signals are close to being periodic on the [[Horizontal scan rate|horizontal scan]] frequency, and thus their [[Spectral density|power spectra]] tends to be concentrated on multiples of such frequency. The specific colour carrier frequency of SECAM results from carefully choosing it so that the [[Harmonic|higher-powered harmonics]] of the modulated chroma and luma signals are apart from each other and from the sound carrier, thereby minimizing [[crosstalk]] between the three signals.

The [[colour space]] perceived by humans is three-dimensional because of the nature of their [[retina]]s, which include specific detectors for red, green and blue light. So in addition to luminance, which is already carried by the existing monochrome signal, colour requires sending two additional signals. The human retina is more sensitive to green light than to red (3:1) or blue (9:1) light. Because of this, the red (<math>R</math>) and blue (<math>B</math>) signals are usually chosen to be sent along luma but with comparably less resolution, to be able to save bandwidth while impacting the perceived image quality the least. (Also, the green signal is on average more closely correlated to luma, making them a poor choice of signal to send separately). To minimize crosstalk with luma and increase compatibility with existing monochrome TV sets, the <math>R</math> and <math>B</math> signals are usually sent as differences from luma (<math>Y</math>): <math>R-Y</math> and <math>B-Y</math>. This way, for an image that contains little colour, its colour difference signals tend to zero and its colour-encoded signal converges to its equivalent monochrome signal.

=== Colourimetry ===
SECAM [[colourimetry]] was similar to PAL, as defined by the ITU on REC-BT.470.<ref name="auto">{{cite web |title=Recommendation ITU-R BT.470-6 Conventional Television Systems |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |url-status=live |archive-url=https://web.archive.org/web/20220121001941/https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |archive-date=21 January 2022 |access-date=21 January 2022}}</ref> Yet the same document indicates<ref name=":0">{{cite web |title=Recommendation ITU-R BT.470-6 Conventional Television Systems, page 16 |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf#page=16 |url-status=live |archive-url=https://web.archive.org/web/20220125063006/https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf#page=16 |archive-date=25 January 2022 |access-date=15 February 2022}}</ref> that for existing (at the time of revision, 1998) SECAM sets, the following parameters (similar to the original 1953 colour NTSC specification<ref>47 CFR § 73.682 (20) (iv)</ref>) could be allowed:
{| class="wikitable"
|+ SECAM colourimetry<ref name="auto" /><ref name=":0" />
! rowspan="2" | Standard
! colspan="2" | [[Standard illuminant#White points of standard illuminants|White point]]
! [[Correlated color temperature|CCT]]
! colspan="6" | [[Primary colors]] (CIE 1931 xy)
! rowspan="2" | Display [[Gamma correction|gamma]] [[EOTF]]
|-
! x
! y
! k
! R<sub>x</sub>
! R<sub>y</sub>
! G<sub>x</sub>
! G<sub>y</sub>
! B<sub>x</sub>
! B<sub>y</sub>
|-
| [[EBU]] 3213-E, [[Rec. 601|ITU-R BT.470/601 (B/G)]]<ref>{{cite web |title=ITU-R BT.470-6 - Conventional Television Systems |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |url-status=live |archive-url=https://web.archive.org/web/20220121001941/https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |archive-date=21 January 2022 |access-date=21 January 2022}}</ref>
| style="background:#{{Color temperature|6500|hexval}}" | 0.3127
| style="background:#{{Color temperature|6500|hexval}}" | 0.3290
| style="background:#{{Color temperature|6500|hexval}}" | 6500 ([[Standard illuminant#Illuminant series D|D65]])
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.64,0.33}});" | 0.64
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.64,0.33}});" | 0.33
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.29,0.60}});" | 0.29
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.29,0.60}});" | 0.60
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.15,0.06}});" | 0.15
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.15,0.06}});" | 0.06
| rowspan="2" | 2.8
|-
| ITU-R BT.470-6 (provisional)<ref name=":0" />
| style="background:#{{Color temperature|6774|hexval}}"  | 0.31
| style="background:#{{Color temperature|6774|hexval}}"  | 0.316
| style="background:#{{Color temperature|6774|hexval}}"  | 6774 ([[Standard illuminant#Illuminants B and C|C]])
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.67,0.33}});" | 0.67
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.67,0.33}});" | 0.33
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.21,0.71}});" | 0.21
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.21,0.71}});" | 0.71
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.14,0.08}});" | 0.14
| style="background-color: color(rec2020 {{CIE xy to BT2020|0.14,0.08}});" | 0.08
|}

The assumed [[display gamma]] was also defined as 2.8.<ref name="auto" />

[[Luma (video)|Luma]] (<math>E'{\scriptstyle\text{Y}}</math>) is derived from red, green, and blue (<math>E'{\scriptstyle\text{R}}, E'{\scriptstyle\text{G}}, E'{\scriptstyle\text{B}}</math>) gamma pre-corrected primary signals:<ref name="auto" />
* <math>E'{\scriptstyle\text{Y}}= 0.299E'{\scriptstyle\text{R}} + 0.587E'{\scriptstyle\text{G}} + 0.114E'{\scriptstyle\text{B}}</math>

<math>D'{\scriptstyle\text{R}}</math> and <math>D'{\scriptstyle\text{B}}</math> are red and blue colour difference signals, used to calculate chrominance:<ref name="auto" />
* <math>D'{\scriptstyle\text{R}}=-1.902(E'{\scriptstyle\text{R}}-E'{\scriptstyle\text{Y}})</math>
* <math>D'{\scriptstyle\text{B}} = +1.505(E'{\scriptstyle\text{B}}-E'{\scriptstyle\text{Y}})</math>

=== Comparison to PAL and NTSC ===
SECAM differs significantly from the other colour systems by the way the colour difference signals are carried. In [[NTSC]] and [[PAL]], each line carries colour difference signals encoded using [[quadrature amplitude modulation]] (QAM). To demodulate such a signal, knowledge of the [[Phase (waves)|phase]] of the [[carrier signal]] is needed. This information is sent along the video signal at the start of every scan line in the form of a short burst of the colour carrier itself, called a "[[colourburst]]". A phase error during QAM demodulation produces crosstalk between the colour difference signals. On NTSC this creates [[Hue]] and [[colorfulness|Saturation]] errors, manually corrected for with a "tint" control on the receiving TV set; while PAL only suffers from Saturation errors. SECAM is free of this problem.

SECAM uses [[frequency modulation]] (FM) to encode chrominance information on the colour carrier, which does not require knowledge of the carrier phase to demodulate. However, the simple FM scheme used allows the transmission of only one signal, not the two required for colour. To address this, SECAM broadcasts <math>R-Y</math> and <math>B-Y</math> separately on alternating [[scan line]]s. To produce full colour, the colour information on one scan line is briefly stored in an [[analogue delay line]] adjusted so the signal exits the delay at the precise start of the next line. This allows the television to combine the <math>R-Y</math> signal transmitted on one line with the <math>B-Y</math> on the next and thereby produce a [[Gamut|full colour gamut]] on every line. Because SECAM transmits only one chrominance component at a time, it is free of the colour artifacts ("[[dot crawl]]") present in NTSC and PAL that result from the combined transmission of colour difference signals.

This means that the vertical colour resolution of a field is halved compared to NTSC. However, the colour signals of all colour TV systems of the time were encoded in a narrower band than their luma signals, so colour information had lower horizontal resolution compared to luma in all systems. This matches the human retina, which has higher luminance resolution than colour resolution. On SECAM, the loss of vertical colour resolution makes the colour resolution closer to uniform in both axes and has little visual effect. The idea of reducing the vertical colour resolution comes from Henri de France, who observed that colour information is approximately identical for two successive lines. Because the colour information was designed to be a cheap, backward-compatible addition to the monochrome signal, the colour signal has a lower bandwidth than the luminance signal, and hence lower horizontal resolution. Fortunately, the human visual system is similar in design: it perceives changes in luminance at a higher resolution than changes in chrominance, so this asymmetry has minimal visual impact. It was therefore also logical to reduce the vertical colour resolution. A similar paradox applies to the vertical resolution in television in general: reducing the bandwidth of the video signal will preserve the vertical resolution, even if the image loses sharpness and is smudged in the horizontal direction. Hence, video could be sharper vertically than horizontally. Additionally, transmitting an image with too much vertical detail will cause annoying flicker on interlaced television screens, as small details will only appear on a single line (in one of the two interlaced fields), and hence be refreshed at half the frequency. (This is a consequence of [[interlaced scanning]] that is obviated by [[progressive scan]].) Computer-generated text and inserts have to be carefully [[low-pass filter]]ed to prevent this.

The colour difference signals in SECAM are calculated in the [[YDbDr]] colour space, which is a scaled version of the [[YUV]] colour space. This encoding is better suited to the transmission of only one signal at a time. [[FM modulation]] of the colour information allows SECAM to be completely free of the [[dot crawl]] problem commonly encountered with the other analog standards. SECAM transmissions are more robust over longer distances than NTSC or PAL. However, owing to their FM nature, the colour signal remains present, although at reduced amplitude, even in monochrome portions of the image, thus being subject to stronger cross colour even though colour crawl of the PAL type does not exist. Though most of the pattern is removed from PAL and NTSC-encoded signals with a [[comb filter]] (designed to segregate the two signals where the luma spectrum may overlap into the spectral space used by the chroma) by modern displays, some can still be left in certain parts of the picture. Such parts are usually sharp edges on the picture, sudden colour or brightness changes along the picture or certain repeating patterns, such as a checker board on clothing. FM SECAM is a [[spectrum (physical sciences)|continuous spectrum]], so unlike PAL and NTSC even a perfect digital comb filter could not entirely separate SECAM luminance and colour signals.

=== Disadvantages ===
{{Unreferenced|section|date=May 2024}}
Unlike PAL or NTSC, analog SECAM programming cannot easily be edited in its native analog form. Because it uses frequency modulation, SECAM is not linear with respect to the input image (this is also what protects it against signal distortion), so electrically mixing two (synchronized) SECAM signals does not yield a valid SECAM signal, unlike with analog PAL or NTSC. For this reason, to mix two SECAM signals, they must be demodulated, the demodulated signals mixed, and are remodulated again. Hence, [[post-production]] is often done in PAL, or in component formats, with the result encoded or transcoded into SECAM at the point of transmission. Reducing the costs of running television stations is one reason for some countries' switchovers to PAL.

Most TVs currently sold in SECAM countries support both SECAM and [[PAL]], and more recently [[composite video]] NTSC as well (though not usually [[broadcast]] NTSC, that is, they cannot accept a broadcast signal from an antenna). Although the older analog camcorders ([[VHS]], [[VHS-C]]) were produced in SECAM versions, none of the [[8 mm video format|8 mm]] or Hi-band models ([[S-VHS]], [[S-VHS-C]], and [[8 mm video format#Hi8|Hi-8]]) recorded it directly. Camcorders and VCRs of these standards sold in SECAM countries are internally PAL. The result could be converted back to SECAM in some models; most people buying such expensive equipment would have a multistandard TV set and as such would not need a conversion. Digital camcorders or DVD players (with the exception of some early models) do not accept or output a SECAM analog signal. However, this is of dwindling importance: since 1980 most European domestic video equipment uses French-originated [[SCART]] connectors, allowing the transmission of [[RGB]] signals between devices. This eliminates the legacy of PAL, SECAM, and NTSC colour sub carrier standards.

In general, modern professional equipment is now all-digital, and uses component-based digital interconnects such as [[CCIR 601]] to eliminate the need for any analog processing prior to the final modulation of the analog signal for broadcast. However, large installed bases of analog professional equipment still exist, particularly in third world countries.

== Varieties ==
{{See also|Broadcast television systems#ITU standards}}

=== Broadcast systems L, B/G, D/K, H, K, M ===
There are six varieties of SECAM, according to each of the [[Broadcast television systems#ITU standards|broadcast system]] it was used with:
* '''SECAM-[[CCIR System L|L]]''': Used only in [[France]], [[Luxembourg]] (only [[RTL9]] on channel 21 from [[Dudelange Radio Tower|Dudelange]]) and [[Télé Monte-Carlo]] transmitters in the south of France.
* '''SECAM-[[CCIR System B|B]]/[[CCIR System G|G]]''': Used in parts of the [[Middle East]], former [[East Germany]], [[Greece]], and [[Cyprus]]
* '''SECAM-[[CCIR System D|D]]/[[CCIR System K|K]]''': Used in the [[Commonwealth of Independent States]] and most parts of [[Central and Eastern Europe]] (this is simply SECAM used with the D and K monochrome TV transmission standards) although most Central and Eastern European countries have now migrated to other systems.
* '''SECAM-[[CCIR System H|H]]''': Around 1983–1984 a new colour identification standard ("Line SECAM or SECAM-H") was introduced in order to make more space available inside the signal for adding [[teletext]] information (originally according to the [[Antiope (teletext)|Antiope]] standard). Identification bursts were made per-line (like in PAL) rather than per-picture. Very old SECAM TV sets might not be able to display colour for today's broadcasts, although sets manufactured after the mid-1970s should be able to receive either variant.
* '''SECAM-[[CCIR System K|K]]''': The standard used in [[Overseas France|France's overseas possessions]] (as well as African countries that were once ruled by France) was slightly different from the SECAM used in [[Metropolitan France]]. The SECAM standard used in Metropolitan France used the SECAM-L and a variant of the channel information for VHF channels 2–10. French overseas possessions and many [[African French|French-speaking African]] countries use the SECAM-[[CCIR System K#System K1|K<sup>1</sup>]] standard and a mutually incompatible variant of the channel information for VHF channels 4-9 (not channels 2–10).
* '''SECAM-[[CCIR System M|M]]''': Between 1970 and 1991, SECAM-M was used in [[Cambodia]],<ref>{{cite book |url=https://www.cisco.com/c/dam/en/us/solutions/service-provider/industry/cable/pdfs/broadband-data-book.pdf |title=Broadband Data Book |date=August 2019 |publisher=Cisco |pages=31 |access-date=17 January 2024 |archive-url=https://web.archive.org/web/20230321004717/https://www.cisco.com/c/dam/en/us/solutions/service-provider/industry/cable/pdfs/broadband-data-book.pdf |archive-date=21 March 2023 |url-status=live}}</ref> [[Laos]], and [[Vietnam]] ([[Hanoi]] and other northern cities).

=== MESECAM (home recording) ===
MESECAM is a method of recording SECAM colour signals onto [[VHS]] or [[Betamax]] video tape. It should not be mistaken for a broadcast standard.

"Native" SECAM recording (marketing term: "SECAM-West") was devised for machines sold for the French (and adjacent countries) market. At a later stage, countries where both PAL and SECAM signals were available developed a cheap method of converting PAL video machines to record SECAM signals, using only the PAL recording circuitry. Although being a workaround, MESECAM is much more widespread than "native" SECAM. It has been the only method of recording SECAM signals to VHS in almost all countries that used SECAM, including the Middle East and all countries in Eastern Europe.

A tape produced by this method is not compatible with "native" SECAM tapes as produced by VCRs in the French market. It will play in black and white only, the colour is lost. Most VHS machines advertised as "SECAM capable" outside France can be expected to be of the MESECAM variety only.

==== Technical details ====
On VHS tapes, the [[Luma (video)|luminance]] signal is recorded FM-encoded (on VHS with reduced bandwidth, on [[S-VHS]] with full bandwidth) but the PAL or NTSC [[chrominance]] signal is too sensitive to small changes in frequency caused by inevitable small variations in tape speed to be recorded directly. Instead, it is first shifted down to the lower frequency of 630&nbsp;kHz, and the complex nature of the PAL or NTSC sub-carrier means that the down conversion must be done via [[heterodyning]] to ensure that information is not lost.

The SECAM sub-carriers, which consist of two simple FM signals at 4.41&nbsp;MHz and 4.25&nbsp;MHz, do not need this (actually simple) processing. The VHS specification for "native" SECAM recording specifies that they be divided by 4 on recording to give sub carriers of approximately 1.1&nbsp;MHz and 1.06&nbsp;MHz, and multiplied by 4 on playback. A true dual-standard PAL and SECAM video recorder therefore requires two colour processing circuits, adding to complexity and expense. Since some countries in the [[Middle East]] use PAL and others use SECAM, the region has adopted a shortcut, and uses the PAL mixer-downconverter approach for both PAL and SECAM, simplifying [[VCR]] design.

Many PAL VHS recorders have had their analog tuner modified in French-speaking western Switzerland (Switzerland used the PAL-B/G standard while the bordering France used SECAM-L). The original tuner in those PAL recorders allows only PAL-B/G reception. The Swiss importers added a circuit with a specific [[Integrated circuit|IC]] for the French SECAM-L standard, making the tuner [[Multi-standard television|multi-standard]] and allowing the VCR to record SECAM broadcasts in MESECAM. A stamp mentioning "PAL+SECAM" was added to these machines.

Video recorders like Panasonic NV-W1E (AG-W1-P for professional), AG-W3, NV-J700AM, Aiwa HV-MX100, HV-MX1U, Samsung SV-4000W and SV-7000W feature a digital standard conversion circuitry.

== Adoption ==
A legacy list of SECAM users in 1998 is available on ''Recommendation ITU-R BT.470-6 - Conventional Television Systems, Appendix 1 to Annex 1'',<ref>{{cite book |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |title=Recommendation ITU-R BT.470-6 - Conventional Television Systems |publisher=ITU Radiocommunication Assembly |year=1998 |pages=29–34 |access-date=21 January 2022 |archive-url=https://web.archive.org/web/20220121001941/https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |archive-date=21 January 2022 |url-status=live}}</ref> and the list before many OIRT countries migrated to PAL can be found at ''CCIR Report 624-3 Characteristics of television systems, Annex I''.<ref>{{cite book |url=https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.282.43.en.1014.pdf |title=Recommendations and Reports of the CCIR, 1986 Volume XI - Part 1 Broadcasting Service (Television) |publisher=CCIR |year=1986 |pages=28–31 |chapter=Report 624-3 Characteristics of television systems, Annex I Systems used in various countries/geographical areas |access-date=28 July 2023 |archive-url=https://web.archive.org/web/20211109083915/https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.282.43.en.1014.pdf |archive-date=9 November 2021 |url-status=live}}</ref>

Below is an updated list of nations that currently authorize the use of the SECAM standard for television broadcasting. It is subject to ongoing changes as nations move to PAL and [[DVB-T]]. These migrations are listed separately.

{| class="wikitable"
! SECAM users
|-
| style="width:50%;" | {{div col|colwidth=19em}}
* {{flag|Benin}}<ref name="HegartyPhelan1998" />
* {{flag|Burkina Faso}}<ref name="HegartyPhelan1998" />
* {{flag|Burundi}}<ref name="HegartyPhelan1998" />
* {{flag|Central African Republic}}<ref name="HegartyPhelan1998" />
* {{flag|Chad}}<ref name="HegartyPhelan1998" />
* {{flag|Republic of the Congo}}<ref name="HegartyPhelan1998" />
* {{flag|Democratic Republic of the Congo}}<ref name="HegartyPhelan1998" />
* {{flag|Gabon}}
* {{flag|Guinea}}<ref name="HegartyPhelan1998" />
* {{flag|Ivory Coast}}<ref name="HegartyPhelan1998" />
* {{flag|Kazakhstan}}<ref name="HegartyPhelan1998" />
* {{flag|Madagascar}}<ref name="HegartyPhelan1998" />
* {{flag|Mali}}<ref name="HegartyPhelan1998" />
* {{flag|Mauritania}}<ref name="HegartyPhelan1998" />
* {{flag|Niger}}<ref name="HegartyPhelan1998" />
* {{flag|Rwanda}}<ref name="HegartyPhelan1998" />
* {{flag|Russia}} (first two multiplex channels transitioned to [[DVB-T2]] in 2019; full transition scheduled for 19 August 2025)<ref>{{cite web |date=2024-08-27 |title=Аналоговое вещание в России продлили ещё на два года |url=https://3dnews.ru/1110062/gkrch-eshchyo-na-dva-goda-prodlila-litsenzii-na-analogovoe-veshchanie |access-date=2024-09-03 |website=3DNews |language=ru}}</ref>
* {{flag|Senegal}}<ref name="HegartyPhelan1998" />
* {{flag|Syria}} (Simulcast in [[PAL]]-G)<ref name="shop.sandbag.uk.com">[http://shop.sandbag.uk.com/OneGiantLeap/PALNTSCInfo.html shop.sandbag.uk.com] {{webarchive |url=https://web.archive.org/web/20160221173323/http://shop.sandbag.uk.com/OneGiantLeap/PALNTSCInfo.html |date=21 February 2016}}</ref>
* {{flag|Tajikistan}}<ref name="HegartyPhelan1998" />
* {{flag|Togo}}<ref name="HegartyPhelan1998" />
* {{flag|Turkmenistan}}<ref name="HegartyPhelan1998" />
{{div col end}}
|}

=== Migration to other standards ===

==== PAL ====
; Europe
{{div col|colwidth=20em}}
* {{flag|Bulgaria}}<ref name="HegartyPhelan1998" /> (Migrated in 1994–1996)
* {{flag|Czechoslovakia}} (Migrated in 1992–1994){{efn|As separate countries ([[Czech Republic]] and [[Slovakia]]) in 1993.}}
* {{flag|East Germany}} (Switchover on 31 December 1991, after [[German reunification]] in 1990){{Citation needed|date=May 2024}}
* {{flag|Estonia}}<ref name="HegartyPhelan1998" /> (Switchover ended in November 1999 with ETV and Kanal 2){{efn|TV3 went to PAL in 1998 and TV1 was in PAL from the beginning.}}
* {{flag|Georgia (country)}}<ref name="HegartyPhelan1998" /> (Migrated in 2000s)
* {{flag|Greece}}<ref name="HegartyPhelan1998" /> (Migrated in 1992)
* {{flag|Hungary}}<ref name="HegartyPhelan1998" /> (Migrated in 1995–1996)
* {{flag|Latvia}}<ref name="HegartyPhelan1998" /> (Migrated in 1997–1999)
* {{flag|Lithuania|1988}} (Migrated in 2002)
* {{flag|Poland}} (Migrated in 1993–1995)
* {{flag|Ukraine}} (Migrated in 1992–1994, simulcast in SECAM until early 2010s)<ref name="HegartyPhelan1998" />
{{div col end}}

[[Czech Republic]], [[Slovakia]], [[Hungary]], and the Baltic countries also changed their underlying sound carrier standard on the UHF band from D/K to B/G which is used in most of Western Europe, to facilitate use of imported broadcast equipment, while leaving the D/K standard on VHF. This required viewers to purchase multistandard receivers though. The other countries mentioned kept their existing standards (B/G in the cases of East Germany and Greece, D/K for the rest).<ref>{{cite web |url=http://tech.ebu.ch/docs/i/i033.pdf |title=Changes to terrestrial television systems in Central and Eastern European countries |access-date=23 February 2010 |archive-date=17 July 2011 |archive-url=https://web.archive.org/web/20110717135202/http://tech.ebu.ch/docs/i/i033.pdf |url-status=live}}</ref>

; Africa
* {{flag|Egypt}}<ref name="HegartyPhelan1998" /> (for a few years before was simulcast){{efn|Ceased in 1992 in favour of [[PAL]]-B/G.}}

; Asia
{{div col|colwidth=20em}}
* {{flag|Afghanistan|1992}} (Migrated in the 1990s)<ref name="HegartyPhelan1998">{{cite book |author1=Michael Hegarty |url=https://books.google.com/books?id=5YjHecPlPS8C&pg=PA260 |title=Classrooms for Distance Teaching and Learning: A Blueprint |author2=Anne Phelan |author3=Lisa Kilbride |date=1 January 1998 |publisher=Leuven University Press |isbn=978-90-6186-867-5 |pages=260–}}</ref>
* {{flag|Armenia}} (Migrated in late 1980s)
* {{flag|Azerbaijan}}<ref name="HegartyPhelan1998" /> (Migrated in 2001)
* {{flag|Cambodia|1989}}<ref name="shop.sandbag.uk.com" /> (Migrated in 1991–1992, from SECAM-M to PAL-B/G)
* {{flag|Iran}}<ref name="shop.sandbag.uk.com" /> (Reverted in 1998 to PAL-B/G)
* {{flag|Laos}} (Migrated in the 1990s from SECAM-M)
* {{flag|North Korea}} (Migrated in 1993)<ref name="HegartyPhelan1998" />
* {{flag|Saudi Arabia}} (Simulcast in NTSC, SECAM, and PAL before switching to PAL entirely in the late 1990s or early 2000s){{Citation needed|date=December 2023}}
* {{flag|Vietnam}} (Brief simulcast in [[PAL]]){{efn|Migrated in the 1990s, from SECAM-M to PAL-D/K.}}
{{div col end}}

==== DVB ====
{| class="wikitable sortable"
! Country
! Switched to
! Switchover completed
|-
| {{FRA}}
| [[DVB-T]]
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{GUF}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{PYF}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{GLP}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{KGZ}}
| [[DVB-T2]]
| <span style="display:none">2015</span>2015
|-
| {{MTQ}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{MUS}}
| DVB-T and DVB-T2
| <span style="display:none">2013</span>2013
|-
| {{MYT}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{MCO}}
| DVB-T
| <span style="display:none">2011-05-24</span>24 May 2011
|-
| {{MAR}}
| DVB-T
| <span style="display:none">2015</span>2015
|-
| {{NCL|size=43px}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{REU}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{BLM}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{SPM}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|-
| {{TUN}}
| DVB-T
| <span style="display:none">2015</span>2015
|-
| {{UZB}}
| DVB-T and DVB-T2
| <span style="display:none">2015</span>2015
|-
| {{WLF}}
| DVB-T
| <span style="display:none">2011-11-29</span>29 November 2011
|}

== See also ==
* {{anl|576i}}

== Notes ==
{{notelist}}

== References ==
{{reflist}}

== External links ==
{{Commons category|SECAM}}
* [http://www.nmia.com/~roberts/vidstd Simple explanation of colour standards]
* [http://digital8.free.fr/video/video.htm Discussion of recording SECAM vs PAL on VHS] (in French)

{{TV resolution}}
{{Video formats}}
{{Color space}}
{{Analogue TV transmitter topics}}
{{Telecommunications}}

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[[Category:ITU-R recommendations]]
[[Category:Standards of France]]
[[Category:Standards of Russia]]
[[Category:Television in France]]
[[Category:Television in the Soviet Union]]
[[Category:Television technology]]
[[Category:Television terminology]]
[[Category:Television transmission standards]]
[[Category:Video formats]]
[[Category:Video signal]]
[[Category:French inventions]]